46 CFR § 71.50-3 - Drydock examination, internal structural examination, underwater survey, and alternate hull exam intervals.
(a) If your vessel is operated on international voyages, it must undergo a drydock and internal structural examination once every 12 months unless it has been approved to undergo an underwater survey per § 71.50–5 of this part.
(b) If your vessel is operated on other than international voyages and does not meet the conditions in paragraphs (c) through (f) of this section, it must undergo a drydock and internal structural examination as follows unless it has been approved to undergo an underwater survey per § 71.50–5 of this part:
(1) Except as provided in paragraph (b)(2) of this section, vessels that operate in salt water must undergo two drydock and two internal structural examinations within any five year period. No more than three years may elapse between any two examinations.
(2) Vessels 20 years of age or older that operate in salt water and accommodate overnight passengers must undergo drydock and internal structural examinations at intervals not to exceed 18 months.
(3) Vessels that operate in fresh water at least six months in every 12 month period since the last drydock examination must undergo drydock and internal structural examinations at intervals not to exceed five years.
(c) Vessels with wooden hulls must undergo two drydock and two internal structural examinations within any five year period regardless of the type of water in which they operate. No more than three years may elapse between any two examinations.
(d) If, during an internal structural examination, damage or deterioration to the hull plating or structural members is discovered, the Officer in Charge, Marine Inspection, may require the vessel to be drydocked or otherwise taken out of service to further assess the extent of the damage and to effect permanent repairs.
(e) Each vessel which has not met the applicable examination schedules in paragraphs (a) through (d) of this section because it is on a voyage, must undergo the required examinations upon completion of the voyage.
(f) For a vessel that is eligible per § 71.50–17 and the owner opts for an alternate hull examination with the underwater survey portion conducted exclusively by divers, the vessel must undergo two alternate hull exams and two internal structural exams within any five-year period. If a vessel completes a satisfactory alternate hull exam, with the underwater survey portion conducted predominantly by an approved underwater ROV, the vessel must undergo one alternate hull and one internal structural exam, within any five-year period. The vessel may undergo a drydock exam to satisfy any of the required alternate hull exams.
(g) The Commandant (CG-CVC) may authorize extensions to the examination intervals specified in paragraph (a) through (c) of this section.